The present invention relates to a thin film magnetic head and a method for the fabrication of the same, wherein an improvement has been made to increase the resistance to wear and chapping of the area of contact of the magnetic head with a magnetic information carrier such as a magnetic tape, drum or disc.
The thin film magnetic head to which the present invention pertains is known as a magnetic transducer suited for high density information recording and/or reproduction and various attempts have heretofore been made to improve the electromagnetic transducing characteristic of the thin film magnetic head. However, one of the major problems which is associated with wear and chapping of the contact surface of the thin film magnetic head resulting from the sliding contact with the magnetic information carrier, for example, magnetic tape, has not yet been solved. This problem will now be discussed in more detail with reference to FIGS. 1 and 2 of the accompanying drawings which show, in side sectional and front sectional views, respectively, an exemplary prior art thin film magnetic head of a type having both a common bias layer and a signal conductor layer provided in the magnetic gap thereof.
Referring now to FIGS. 1 and 2, the prior art thin film magnetic head comprises a substrate 1 made of ferrite, for example, and having a first non-magnetic insulating layer 2 formed optionally on one surface of the substrate 1. Provided on the non-magnetic insulating layer 2 are a bias conductor layer 3, a signal conductor layer 4 and a terminal member 5 for electric connection with an external electric circuit (not shown). The conductor layers 3 and 4 are covered by a second non-magnetic insulating layer 6 mounted on the first non-magnetic insulating layer 2, which is in turn overlaid with a thin magnetic layer 7 made of a magnetic material. Overlaying the thin magnetic layer 7 is a third non-magnetic insulating layer 8 to which a retainer plate 9 is bonded by the use of a bonding material 10.
The thin layer magnetic head so fabricated is electrically connected to the external electric circuit through the terminal member 5, and the contact surface of the magnetic head, shown by the broken line 11 in FIG. 1, which, when in use, slidingly contacts a magnetic information carrier, for example, a magnetic tape, is formed by cutting and grinding an unwanted portion of the magnetic head which extends beyond the head contact surface 11.
When the prior art magnetic head of the construction described above is viewed from the head contact surface and, particularly, as shown in FIG. 2, the third non-magnetic insulating layer 8 is seen to have indented portions and, therefore, a considerable amount of the bonding material 10 is considerably exposed. More specifically, since the thickness of the thin magnetic layer 7 has an influence on the efficiency of the magnetic head as a whole, it must have such a value that the thin magnetic layer 7 will not be magnetically saturated. Accordingly, the average thickness required for the thin magnetic layer 7 is generally about 3 .mu.m and, in the case of a thin film magnetic head particularly for use in recording a short wavelength signal, the required thickness of the thin magnetic layer 7 is about 1 .mu.m. The use of a thin magnetic layer 7 of such a thickness results in the indented portions of the third non-magnetic insulating layer 8 being about 1 to 3 .mu.m deep and the consequence is that, as can readily be understood from FIG. 2, the exposed surface area of the deposited bonding material 10 between the retainer plate 9 and the third non-magnetic insulating layer 8 is increased. If the bonding material 10 used is of a type capable of having a relatively high hardness when cured or hardened, there will be no problem of wear and chapping of the head contact surface which may result from the sliding contact with the magnetic tape. For this purpose, a glass is suitable as a bonding material. However, since the glass has a relatively high melting point requiring a relatively high temperature for the glass to reach a fluidized state, the bonding by the use of the glass tends to bring about deterioration in the magnetic characteristic of the finished magnetic head, an increase in the specific resistance of the conductor layers 3 and 4 and/or deterioration in the insulating property of the second non-magnetic insulating layer 6 and, therefore, glass has not yet been employed in practice as the bonding material 10, but instead a synthetic resinous bonding material is largely employed.
If the synthetic resinous bonding material is carefully selected from currently commercially available types and, if necessary, mixed with one or more filler material, the resistance to wear and chapping of the thin film magnetic head can be improved, but only to a certain extent. This is because a life test of a thin film magnetic head wherein resin binder was used has shown that substantially no chapping occurred at the portion 12 of the magnetic head, where substantially no resin binder was applied or, if it was applied was applied in a thickness of about 0.2 .mu.m, while the portion 13 where a relatively large amount of the resin binder was damaged deposited was considerably. The influence of the damage to the portion 13 had extended to the portion 14, located at a leading position relative to the portion 13 with respect to the direction of travel of the magnetic tape shown by the arrow 15, and it has been found that not only were the first, second and third nonmagnetic insulating layers 2, 6 and 8 crumbled, but also respective portions 16 and 17 of the retainer plate 9 and substrate 1 were crumbled. In particular, where the substrate 1 is made of ferrite, the crumbling of the end portion 17 of the substrate 1 resulted in formation of tiny pieces of ferrite which are likely to cause a chapping of the head contact surface during a prolonged use of the thin film magnetic head with the magnetic tape.
As discussed above, the prior art thin film magnetic head having the construction shown in FIGS. 1 and 2 involves various problems associated with reliability and durability.
Although not directed to improvement of resistance to wear and chapping of the head contact surface, U.S. Pat. No. 4,092,688, patented on May 30, 1978 and assigned to the assignee of the present invention, discloses a similar thin film magnetic head.